This invention is a method and apparatus for running spooled tubing into a well, particularly into a hydrocarbon well.
There are a number of techniques for artificially lifting formation liquids from hydrocarbon wells. Reciprocating sucker rod pumps are the most common because they are the most cost effective, all things considered, over a wide variety of applications. Other types of artificial lift include electrically driven down hole pumps, hydraulic pumps, gas lift, rotating rod pumps, and free pistons or plunger lifts. These alternate types of artificial lift are more effective, either in cost or efficiency, than sucker rod pumps in the niches or applications where they have become popular.
Gas wells reach their economic limit for a variety of reasons. A very common reason is the produced gas volume declines to a point where it is insufficient to move formation liquids upwardly to the surface. Two phase upward flow in a well is complicated and most equations thought to predict flow are only rough estimates of what is going on. One reason is the changing relation of the liquid and gas flowing upwardly in the well. At times of more-or-less constant flow, the liquid acts as an upwardly moving film on the inside of the flow string while the gas flows in a central path on the inside of the liquid film. The gas flows much faster than the liquid film. When the volume of gas flow slows below some critical value, the liquid runs down the inside of the flow string and accumulates in the bottom of the well.
If sufficient liquid accumulates in the bottom of the well, the well is no longer able to flow because the pressure in the reservoir is insufficient to cause flow against the pressure of the liquid column. The well is said to have loaded up and died. Years ago, gas wells were plugged much quicker than today because it was not economic to artificially lift small quantities of liquid from a gas well. At relatively high gas prices, it is economic to keep old gas wells on production. It has gradually been realized that gas wells have a life cycle that includes an old age segment where a variety of techniques are used to keep liquids flowing upwardly in the well and thereby prevent the well from loading up and dying.
The appropriate technique for keeping old gas wells flowing depends on where the well is in its life cycle. For example, the first technique is to drop soap sticks into the well. The soap dissolves in the formation liquid and some agitation causes the liquid to foam. The well is then turned to the atmosphere and a great deal of foamed liquid is discharged from the production string. Later in its life cycle, when soaping the well has become ineffective, other techniques such as those listed above are used. Another effective technique is running a velocity string of 1xe2x80x3 or 1xc2xdxe2x80x3 tubing inside the production string so the upward velocity of gas moving in the velocity string is sufficient to keep the liquid moving upwardly.
These techniques all have their advantages and disadvantages. Some techniques work reasonably well but only for a short time and then become ineffective. Some techniques are costly and require substantial maintenance. Some techniques require the well to be reworked by pulling the production string from the well and rerunning it.
Disclosures relevant to this invention are found in U.S. Pat. Nos. 3,260,308; 3,971,437; 4,585,066; 4,673,035; 4,681,169; 5,161,956; 5,180,014; 5,183,391; 5,211,242 and 5,611,671.
In this invention, a pair of tubing strings are simultaneously run into a well for a variety of reasons. One may be to provide a down hole pump of some description, to provide multiple strings for injecting materials into the well and the like.
In a preferred embodiment of this invention, a chamber is run into a well at the end of two strings of spooled tubing, one being a gas supply string and the other being a liquid production string. The spooled tubing strings are run simultaneously into the well at a sufficiently fast rate to land the chamber adjacent the perforations in a relatively short time. The strings are suspended in a landing sub on the well head. The gas supply string is connected to a source of relatively high pressure gas, such as a compressor or high pressure gas system. The liquid production string is connected to conventional production equipment for handling the produced liquid and gas. Typically,. the gas is delivered to a low pressure gas system or to a compressor for delivery to sales.
The chamber is preferably landed below the perforations so there is no liquid buildup above the perforations impeding gas flow to the surface. The system accordingly acts as a downhole gas-liquid separator where gas flows upwardly in the annulus between the production string and the spooled tubing strings and the liquid flows downwardly into the chamber. The chamber includes a check valve allowing flow into the chamber and preventing reverse flow. Gas is delivered down the gas supply string, either periodically or continuously, which pressurizes the chamber and closes the check valve. When gas at sufficient pressure and in sufficient volume is delivered down the gas supply string, the liquid in the chamber is pushed upwardly through the liquid production string and discharges at the surface into the separator. When the supply gas is turned off, the chamber and spooled tubing strings exhaust into the compressor or low pressure gas system which reduces the pressure in the chamber and allows the check valve to open thereby allowing liquid flow into the chamber. The process is repeated as often as necessary or desirable to keep the well flowing at a commercial rate.
Preferably, the only moving part in the well is the check valve in the chamber, which is made of long lived materials so the apparatus of this invention operates for long periods of time without pulling the spooled tubing strings. Because the chamber is preferably located below the perforations, this invention provides a long term solution to keeping gas wells flowing at commercial rates with minimum maintenance. Because the chamber is preferably located below the perforations, this invention provides the least possible restriction against gas flow from the formation and accordingly provides a liquid lift system that operates effectively from the time of installation to the economic limit of the well. In other words, no further capital costs are needed to produce the well to its economic limit and the well""s economic limit is prolonged to the greatest extent possible.
It is one object of this invention to provide a technique for producing hydrocarbon wells that are prone to load up and die.
A further object of this invention is to provide a technique for simultaneously running multiple strings of spooled tubing into a well.
Another object of this invention is to provide a technique for simultaneously running multiple strings of spooled tubing and a down hole pump into a well.
These and other objects and advantages of this invention will become more apparent as this description proceeds, reference being made to the accompanying drawings and appended claims.